Semimetal compound of Pt and method for making the same

ABSTRACT

The disclosure relates to a semimetal compound of Pt and a method for making the same. The semimetal compound is a single crystal material of PtTe 2 . The method comprises: providing a PtTe 2  polycrystalline material; placing the PtTe 2  polycrystalline material in a reacting chamber; placing chemical transport medium in the reacting chamber; evacuating the reacting chamber to be vacuum less than 10 Pa; placing the reacting chamber in a temperature gradient, wherein the reacting chamber has a first end in a temperature from 1200 degree Celsius to 1000 degree Celsius and a second end opposite to the first end and in a temperature from 1000 degree Celsius to 900 degree Celsius; and keeping the reacting chamber in the temperature gradient for 10 days to 30 days.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 fromChina Patent Application No. 201610552213.4, filed on Jul. 13, 2016, inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference. This application is related toapplications entitled, “METHOD FOR MAKING SEMIMETAL COMPOUND OF Pt”,filed Jul. 6, 2017 Ser. No. 15/642,345.

BACKGROUND 1. Technical Field

The present disclosure relates to a semimetal compound of Pt and methodfor making the same.

2. Description of Related Art

Three-dimensional semimetals are important hosts to exotic physicalphenomenon such as giant diamagnetism, linear quantum magnetoresistance,and quantum spin Hall effect. Three dimensional Dirac fermions can beviewed as three dimensional version of graphene and have been realizedin Dirac semimetals. Cd₃As₂, Na₃Bi, K₃Bi, and Rb₃Bi are found asthree-dimensional Dirac semimetals. However, all the Cd₃As₂, Na₃Bi,K₃Bi, and Rb₃Bi are type-I Dirac semimetals having a vertical cone ofelectron energy band as shown in FIG. 1. The type-I Dirac semimetalsshows spin degenerate conical dispersions that cross at isolatedmomenutum points (Dirac points) in three dimensional momentum space. Ina topological Dirac semimetal, the massless Dirac fermions arestabilized by crystal symmetry and could be driven into varioustopological phases. When breaking the inversion or time-reversalsymmetry, the doubly degenerate Dirac points can be split into a pair ofWeyl points with opposite chiralities, and a Dirac fermion splits intotwo Weyl fermions. Weyl fermions were originally proposed in high energyphysics, and their condensed matter physics counterparts have beenrecently realized. Weyl semimetals exhibit intriging properties, withopen Fermi arcs connecting the Weyl points of opposite chiralities. BothDirac and Weyl semimetals obey Lorentz invariance and they exhibitanomalous negative magnetoresistance.

Recently, a new type of Weyl semimetal (type-II Dirac semimetals) havebeen predicted. In type-II Dirac semimetals, the Weyl points arise fromthe topologically protected touching points between electron and holepockets, and there are finite density of states at the Fermi level.Type-II Dirac semimetals have strongly tilted cone and thus violate theLorantzian invariance. However, so far, the spin-degenerate counterpartof type-II Dirac semimetals have not been realized.

What is needed, therefore, is a type-II Dirac semimetals and method formaking the same that overcomes the problems as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic section views of electron energy band of type-IDirac semimetal and type-II Dirac semimetal.

FIG. 2 is a flowchart of example I of a method for making a semimetalPtTe₂.

FIG. 3 is a schematic section view of example I of a device for making asemimetal PtTe₂.

FIG. 4 is a photo image of the semimetal PtTe₂ of example I.

FIG. 5 is an X-ray diffraction (XRD) result of the semimetal PtTe₂ ofexample I measured at room temperature.

FIG. 6 is a Raman spectrum result of the semimetal PtTe₂ of example Imeasured at room temperature.

FIG. 7 is a low energy electron diffraction (LEED) pattern of thesemimetal PtTe₂ of example I taken at beam energy of 70 eV.

FIG. 8 shows a measured in-plane Dirac cone along MT-K direction of thesemimetal PtTe₂ of example I measured at 22 eV and a calculatedsimulation result.

FIG. 9 shows a measured out-plane Dirac cone along MT-K direction of thesemimetal PtTe₂ of example I measured at 22 eV and a calculatedsimulation result.

FIG. 10 is a flowchart of example II of a method for making a semimetalPtTe₂.

FIG. 11 is a schematic section view of example II of a device for makinga semimetal PtTe₂.

FIG. 12 is a photo image of the semimetal PtTe₂ of example II.

FIG. 13 is an X-ray diffraction (XRD) result of the semimetal PtTe₂ ofexample II measured at room temperature.

FIG. 14 is a Raman spectrum result of the semimetal PtTe₂ of example IImeasured at room temperature.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated better illustratedetails and features. The description is not to be considered aslimiting the scope of the embodiments described herein.

The term “outside” refers to a region that is beyond the outermostconfines of a physical object. The term “inside” indicates that at leasta portion of a region is partially contained within a boundary formed bythe object. The term “substantially” is defined to essentiallyconforming to the particular dimension, shape or other word thatsubstantially modifies, such that the component need not be exact. Forexample, substantially cylindrical means that the object resembles acylinder, but can have one or more deviations from a true cylinder. Theterm “comprising” means “including, but not necessarily limited to”; itspecifically indicates open-ended inclusion or membership in aso-described combination, group, series and the like. It should be notedthat references to “an” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

References will now be made to the drawings to describe, in detail,various embodiments of the present type-II Dirac semimetals and methodfor making the same.

Example I

Referring to FIGS. 2-3, a self-flux method for making the semimetalPtTe₂ comprises following steps:

-   -   step (S10), placing pure Pt and pure Te in a reacting chamber 10        as reacting materials 13;    -   step (S11), evacuating the reacting chamber 10 to a vacuum less        than 10 Pa;    -   step (S12), heating the reacting chamber 10 to a first        temperature from 600 degree Celsius to 800 degree Celsius and        keeping the first temperature for a period from about 24 hours        to about 100 hours;    -   step (S13), cooling the reacting chamber 10 to a second        temperature from 400 degree Celsius to 500 degree Celsius and        keeping the second temperature for a period from about 24 hours        to about 100 hours at a cooling rate from about 1 degree Celsius        per hour to about 10 degree Celsius per hour to obtain a        reaction product 15 comprising a crystal material of PtTe₂; and    -   step (S14), separating the crystal material of PtTe₂ from the        reaction product 15.

In step (S10), the reacting chamber 10 is a quartz tube having an openend and a sealed end opposite to the open end. The quartz tube is filledwith quartz slag 11 so that the quartz slag 11 to form a supporter atthe sealed end. The supporter has a thickness in a range from about 0.5centimeter to about 3 centimeters. In one embodiment, the thickness ofthe supporter is about 2 centimeters. The particle diameter of thequartz slag 11 is less than 1 millimeter. The inner diameter of thequartz tube is about 8 millimeters, and the outer diameter of the quartztube is about 10 millimeters. The quartz tube is further filled withquartz wool 12 so that the quartz wool 12 to form a filter on the quartzslag 11. The filter has a thickness in a range from about 0.5 centimeterto about 2 centimeters. In one embodiment, the thickness of the filteris about 1 centimeter. The diameter of the quartz wool 12 can be in arange from about 1 micrometer to about 10 micrometers. In oneembodiment, the diameter of the quartz wool 12 is about 4 micrometers.The quartz slag 11 and the quartz wool 12 are used to separate thecrystal material of PtTe₂ from the reaction product 15. The quartz slag11 and the quartz wool 12 are optional. If the quartz slag 11 and thequartz wool 12 are omitted, the reaction product 15 should be separatedby special method. The pure Pt and pure Te are filled in the quartz tubeafter the quartz tube is filled with the quartz slag 11 and the quartzwool 12. The molar ratio of Pt element and Te element is about2:80˜2:120. In one embodiment, Pt:Te=2:98. The pure Pt and pure Te formthe reacting materials 13. The purity of pure Pt is greater than 99.9%,and the purity of pure Te is greater than 99.99%.

In step (S11), the quartz tube is evacuated by a mechanical pump andthen the open end of the quartz tube is sealed by fast heating the openend by a flame of natural gas and oxygen gas. In one embodiment, thepressure of the quartz tube can be less than 1 Pa. The natural gas canbe replaced by propane gas or hydrogen gas.

In step (S12), the quartz tube is reversed and vertically located sothat the reacting materials 13 is located at the bottom of the quartztube, and the quartz slag 11 and the quartz wool 12 are located at thetop of the quartz tube. The quartz tube is further accommodated in asteel sleeve 14. The fire-resistant cotton is filled between the quartztube and the steel sleeve 14 to fix and keep the temperature of thereaction product 15 in the quartz tube.

The steel sleeve 14, having the quartz tube therein, is placed in amuffle furnace. The quartz tube is heated to 700 degree Celsius and keptfor 48 hours at 700 degree Celsius in the muffle furnace. Duringheating, the reacting material 13 is kept at the bottom of the quartztube and the quartz slag 11 and the quartz wool 12 are kept at the topof the quartz tube. The quartz tube can also be heated by other heatingdevice rather than muffle furnace.

In step (S13), in one embodiment, the muffle furnace is cooled down to480 degree Celsius at a cooling rate of 5 degree Celsius per hour andkept for 48 hours at 480 degree Celsius to obtain the reaction product15. The reaction product 15 includes the crystal material of PtTe₂ andthe excessive reacting materials. The cooling rate can be in a rangefrom about 1 degree Celsius per hour to about 10 degree Celsius perhour.

In step (S14), the steel sleeve 14, having the quartz tube therein, istaken out from the muffle furnace. Then the steel sleeve 14 is reversedand vertically located so that the quartz slag 11 and the quartz wool 12are located at the bottom of the quartz tube, and the reaction product15 is filed by the quartz wool 12. Thus, the excessive reactingmaterials is separated from the crystal material of PtTe₂.

Furthermore, the steel sleeve 14, having the quartz tube therein, can becentrifugalized for a period in a range from about a minutes to about 5minutes at a speed in a range from about 2000 rpm/m to about 3000 rpm/m.In one embodiment, the centrifugalization period is about 2 minutes, andthe centrifugalization speed is about 2500 rpm/m. The excessive reactingmaterials can also be separated from the crystal material of PtTe₂ byother method after the reaction product 15 is taken out of the quartztube.

The quartz tube is taken out of the steel sleeve 14 after naturalcooling. Then the crystal material of PtTe₂ is taken out of the quartztube, washed by chemical reagent to remove the residual Te element, andthen rinsed by water to obtain pure crystal material of PtTe₂. Thechemical reagent can be hydrogen peroxide, dilute hydrochloric acid,sodium hydroxide.

The pure crystal material of PtTe₂ of example I was tested. FIG. 4 is aphoto image of the semimetal PtTe₂ of example I. As shown in FIG. 4, thesemimetal PtTe₂ of example I is macroscopic visible and has a lengthabout 5 millimeters and a thickness about 10 micrometers to about 100micrometers. FIG. 5 is a XRD result of the semimetal PtTe₂ of example Imeasured at room temperature. FIG. 6 is a Raman spectrum result of thesemimetal PtTe₂ of example I measured at room temperature. FIG. 7 is aLEED pattern of the semimetal PtTe₂ of example I taken at a beam energyof 70 eV. As shown in FIGS. 5 and 7, the semimetal PtTe₂ of example Iconfirm the high quality of the single crystals. As shown in FIG. 7, thesemimetal PtTe₂ of example I has a symmetrical structure. The Ramanspectrum in FIG. 6 shows Eg and A1g vibrational modes of the semimetalPtTe₂ of example I at about 110 cm⁻¹ and 157 cm⁻¹ respectively, whichare typical for 1 T structure.

FIG. 8 shows a measured in-plane Dirac cone along MT-K direction of thesemimetal PtTe₂ of example I measured at 22 eV and a calculatedsimulation result. FIG. 9 shows a measured out-plane Dirac cone alongMT-K direction of the semimetal PtTe₂ of example I measured at 22 eV anda calculated simulation result. As shown in FIGS. 8-9, it isexperimentally and theoretically confirm that the semimetal PtTe₂ ofexample I belong to Type-II Dirac semimetals. The semimetal PtTe₂ ofexample I has wonderfully physical properties such as negativemagnetoresistance, quantum spin Hall effect, or linear quantummagnetoresistance. As Type-II Dirac semimetals, the semimetal PtTe₂ ofexample I exhibits anomalous negative magnetoresistance.

Example II

Referring to FIGS. 10-11, a chemical vapor transport method for makingthe semimetal PtTe₂ comprises following steps:

-   -   step (S20), providing a PtTe₂ polycrystalline material;    -   step (S21), placing the PtTe₂ polycrystalline material in a        reacting chamber 20 as reacting materials 23;    -   step (S22), placing chemical transport medium 26 in the reacting        chamber 20;    -   step (S23), evacuating the reacting chamber 20 to be vacuum less        than 10 Pa;    -   step (S24), placing the reacting chamber 20 in a temperature        gradient, wherein the reacting chamber 20 has a first end 201 in        a temperature from about 1200 degree Celsius to about 1000        degree Celsius and a second end 202 opposite to the first end        201 and in a temperature from about 1000 degree Celsius to about        900 degree Celsius; and    -   step (S25), keeping the reacting chamber 20 in the temperature        gradient for 10 days to 30 days to obtain the reaction product        25 at the second end 202.

In FIG. 11, AB represents the element of PtTe₂, and L represents theelement of the chemical transport medium 26.

In step (S20), the PtTe₂ polycrystalline material can be provided by anymethod. In one embodiment, the PtTe₂ polycrystalline material is made byfollowing steps:

-   -   step (S201), placing pure Pt and pure Te in a quartz tube as        reacting materials, wherein the molar ratio Pt:Te=1:2, the        purity of pure Pt is greater than 99.9%, and the purity of pure        Te is greater than 99.9%;    -   step (S201), evacuating the quartz tube to be vacuum less than        10 Pa and the quartz tube is sealed by fast heating;    -   step (S203), heating the quartz tube to a reacting temperature        from 750 degree Celsius to 850 degree Celsius and keeping the        reacting temperature for a period from about 50 hours to about        100 hours to obtain the PtTe₂ polycrystalline material; and    -   step (S204), cooling the quartz tube to room temperature at a        cooling rate in a range from about 10 degree Celsius per hour to        about 20 degree Celsius per hour and taking the PtTe₂        polycrystalline material out of the quartz tube.

In step (S204), the PtTe₂ would be kept as polycrystalline because thecooling rate is higher than 10 degree Celsius per hour.

In step (S21), the reacting chamber 20 is a quartz tube having an openend and a sealed end opposite to the open end. The inner diameter of thequartz tube is about 8 millimeters, and the outer diameter of the quartztube is about 10 millimeters. The reacting materials 23 is located atthe sealed end of the quartz tube.

In step (S22), the chemical transport medium 26 can be located adjacentto the reacting materials 23. The chemical transport medium 26 can beTeBr₄, I₂, Br₂, Cl₂, SeCl₄. The concentration of the chemical transportmedium 26 can be in a range from about 5 mg/mL to about 20 mg/mL. In oneembodiment, the chemical transport medium 26 is TeBr₄ with aconcentration 10 mg/mL.

In step (S23), the quartz tube is evacuated and sealed by fast heatingas described above. The pressure of the quartz tube can be lower than 1Pa.

In step (S24), the quartz tube is horizontally located in the tubularfurnace 27. The reacting materials 23 are located at the first end 201of the quartz tube. The temperature of the first end 201 is higher thanthe temperature of the second end 202 so that the temperature gradientis formed between the first end 201 and the second end 202. In oneembodiment, the first end 201 of the quartz tube is heated to 1050degree Celsius, and the second end 202 of the quartz tube is heated to970 degree Celsius.

In step (S25), the reaction product 25 can be obtained at the second end202 of the quartz tube after keeping the temperature gradient for 10days to 30 days. The reaction product 25 is taken out of the quartz tubeand washed by alcohol to remove the chemical transport medium to obtainpure crystal material of PtTe₂. In one embodiment, the reacting chamber20 is kept in the temperature gradient for 20 days.

The pure crystal material of PtTe₂ of example II is tested. FIG. 12 is aphoto image of the semimetal PtTe₂ of example II. As shown in FIG. 12,the semimetal PtTe₂ of example II is macroscopic visible and has a sizeabout 2 millimeters. FIG. 13 is a XRD result of the semimetal PtTe₂ ofexample II measured at room temperature. FIG. 14 is a Raman spectrumresult of the semimetal PtTe₂ of example II measured at roomtemperature. As shown in FIG. 13, the semimetal PtTe₂ of example IIconfirm the high quality of the single crystals. The Raman spectrum inFIG. 14 shows Eg and A1g vibrational modes of the semimetal PtTe₂ ofexample I at about 110 cm⁻¹ and 157 cm⁻¹ respectively, which are typicalfor 1 T structure. It is experimentally and theoretically confirm thatthe semimetal PtTe₂ of example II belong to Type-II Dirac semimetals.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A semimetal compound of Pt, wherein the semimetalcompound of Pt is single crystal PtTe₂.
 2. The semimetal compound of Ptof claim 1, wherein the single crystal PtTe₂ is type-II Diracsemimetals.
 3. The semimetal compound of Pt of claim 1, wherein thesingle crystal PtTe₂ has tilted Dirac cone.
 4. The semimetal compound ofPt of claim 1, wherein the single crystal PtTe₂ exhibits anomalousnegative magnetoresistance.
 5. A method for making semimetal compound ofPt, the method comprising: placing a PtTe₂ polycrystalline material anda chemical transport medium in a reacting chamber; evacuating thereacting chamber to be vacuum with a pressure lower than 10 Pa; placingthe reacting chamber in a temperature gradient, wherein the reactingchamber has a first end in a first temperature from about 1200 degreeCelsius to about 1000 degree Celsius and a second end opposite to thefirst end and in a second temperature from about 1000 degree Celsius toabout 9000 degree Celsius, and the PtTe₂ polycrystalline material islocated at the first end; and keeping the reacting chamber in thetemperature gradient for 10 days to 30 days.
 6. The method of claim 5,wherein the chemical transport medium is selected from the groupconsisting of TeBr₄, I₂, Br₂, Cl₂, and SeCl₄.
 7. The method of claim 5,wherein a concentration of the chemical transport medium is in a rangefrom about 5 mg/mL to about 20 mg/mL.
 8. The method of claim 5, whereinthe pressure is lower than 1 Pa.
 9. The method of claim 5, wherein thereacting chamber is a quartz tube having an open end and a sealed endopposite to the open end, and the PtTe₂ polycrystalline material islocated at the sealed end.
 10. The method of claim 9, wherein theevacuating the reacting chamber comprises sealing the open end by fastheating.
 11. The method of claim 9, wherein the placing the reactingchamber in the temperature gradient comprises horizontally placing thequartz tube in a tubular furnace.
 12. The method of claim 5, wherein thePtTe₂ polycrystalline material is made by following steps: placing purePt and pure Te in reacting room, wherein a molar ratio is Pt:Te=1:2;evacuating the reacting room to be vacuum less than 10 Pa and sealingthe reacting room; heating the reacting room to a reacting temperaturefrom 750 degree Celsius to 850 degree Celsius and keeping the reactingtemperature for a period from about 50 hours to about 100 hours toobtain the PtTe₂ polycrystalline material; and cooling the reacting roomto room temperature at a cooling rate in a range from about 10 degreeCelsius per hour to about 20 degree Celsius per hour.